The present invention relates to the operation of power tongs of the type commonly used to make up and break apart threaded oilfield tubular connections. More particularly, this invention relates to an improved tong shutdown system and method which reliably ensures that the door of an open throat power tong is properly closed before rotation of the tong rotary ring.
Power tongs or oilfield equipment commonly used to make up and break apart threaded connections on casing, tubing, or other oilfield tubulars. While various types of power tongs have been devised, the type most preferred by many oilfield operators for over fifty years has a tong body or frame with an open throat, and a partial rotary ring or rotary gear with a corresponding throat. When the frame and rotary ring throats are aligned, the power tong may be moved laterally on and off the oilfield tubular. Once the tubular is positioned within the rotary ring, the door attached to the frame is closed and the ring engages the tubular and rotates to make up or break apart the threaded connection.
Because of a need for safety, oilfield equipment operators require guards or doors on the open throat frame of a power tong. If the door is not properly closed before the tong is actuated, an operator hand may accidentally enter the throat area. The high speed rotation of the rotary ring has injured many oilfield operators. In some cases, the worker appendage slips into the area of the rotary ring throat, severely injuring the worker.
Various types of systems have been devised which seek to prevent these injuries, and more particularly allow rotation of the rotary ring only when the tong door is properly closed. When the tong door or guard is opened to allow lateral movement of the power tong onto and off the tubular, the system does not allow rotation of the rotary ring or rotary gear. A common method of accomplishing this goal it utilizes a hydraulic valve adjacent the tong door, with the valve being opened or closed by a pin or other member movably responsive to the door position. The hydraulic valve may be provided with fluid from a line connected to the fluid supply line to the motor, and a return line from the hydraulic valve may be connected to the hydraulic return line from the motor, i.e., the hydraulic tong motor for rotating the rotary ring or gear and the hydraulic valve are fluidly in parallel. When the guard is properly positioned closed, the hydraulic valve is also closed and high pressure fluid is available to power the tong hydraulic motor, thereby rotating the ring. When the door is not properly fully closed, the hydraulic valve is open and bypasses fluid back to the return line. This bypass prevents the buildup of high pressure fluid being supplied to the tong motor, thereby hopefully preventing rotation of the partial ring.
The safety system as described above has several shortcomings which have limited its acceptance, and most importantly have not prevented some accidents to oilfield operators. The prior art system requires additional valves and hoses which must be added to the hydraulic system. These hoses and valves may leak, and in frustration the oilfield operator may bypass this safety system. Moreover, even when the hydraulic valve is opened and fluid is bypassed through the hydraulic valve and returned to the hydraulic power source, some fluid under pressure is still available to drive the power tong motor. Accordingly, the hydraulic valve may be open but the motor may still rotate the ring, although at less than its full speed. Any rotation of the rotary ring or gear with the door not properly closed can be dangerous and may injure the oilfield worker.
In an attempt to overcome the shortcomings of the system described above, another method has been developed for preventing rotation of the rotary ring when the tong door is open. This alternative system completely blocks the flow of fluid to the motor when the hydraulic valve is closed by placing the hydraulic valve and the motor fluidly in series, with the motor downstream from the hydraulic valve. This system has the disadvantage of also requiring additional valves and hoses, thereby making the hydraulic system more complex. As with the system described earlier, the expense of additional valves and hoses and a possibility of fluid leakage encourage the operator to bypass the safety system. Also, this latter system undesirably allows the tong motor to run when the tong door is closed but without an operator intentionally resetting the system. Accordingly, while the tong door should be closed before high pressure fluid to be available to the power tong motor, operator intervention is not required to purposefully initiate or reset the system in order to supply fluid to the power tong motor once the door is closed. If the hydraulic safety valve is accidentally bumped at the same time the motor control valve handle is bumped, the tong motor could restart.
The disadvantages of the prior art are overcome by the present invention, and an improved method and system are hereinafter disclosed for operating a power tong while improving operator safety. The system of the present invention desirably stops rotation of the rotary ring without creeping of the rotary ring in a manner of the system most commonly used in the prior art. Moreover, the system of the present invention does not require altering the conventional fluid delivery system of the tong which supplies fluid pressure from the hydraulic fluid source to the power tong motor.
In a preferred embodiment, the power tong for making up and breaking apart threaded oilfield connections includes a tong frame having a frame open throat, a rotary ring rotatably supported on the tong frame and having a ring open throat, and a door for closing the frame open throat. With the door open, the power tong may be moved laterally on and off an oilfield tubular connection once the ring open throat is aligned with the frame open throat. The ring is powered by a hydraulic motor supported on the frame for rotating the rotary ring. A motor control valve is operable to control flow of high pressure fluid from a high pressure source to the hydraulic motor. A pilot valve or switch supported on the tong frame outputs a signal in response to the position of the door to a valve operator which controls operation of the motor control valve. A hydraulic cylinder or other fluid pressure responsive member automatically engages and disengages operation of the valve operator and thus the motor control valve in response to the signal from the switch. A fluid supply line is provided for supplying pressurized fluid, and preferably a pneumatic pressure, to the switch and then to the fluid pressure responsive member. When the switch outputs a signal indicative of the door being closed to the fluid pressure responsive member, the valve operator is automatically engaged such that the movement of the valve operator controls the motor control valve and thus supplies fluid pressure to the hydraulic motor. When the switch outputs a door open signal to the fluid pressure responsive member, the valve operator is automatically disengaged such that movement of the valve operator does not control operation of the motor control valve. The fluid pressure responsive member is biased in the disengaged position, preferably by a spring, to provide for fail safe operation. In a preferred embodiment, the switch is thus opened to pass pneumatic fluid to the fluid pressure responsive member when the door is closed, and the switch is closed to automatically prevent transmission of pneumatic pressure to the fluid pressure responsive member when the door is opened.
To further enhance reliability of this shutoff system, a pivotal link member is preferably positioned between the door and the switch. The link member thus moves in response to movement of the door to activate and deactivate the switch. This link member allows the switch to be located on the tong frame substantially rearward of the door, and preferably opposite the door with respect to a centerline of the rotary ring. An adjustment screw is provided for controlling the output signal from the switch in response to the position of the link member and thus the position of the door.
As previously noted, the fluid pressure responsive member may be a pneumatic cylinder with a rod which is extended in response to pneumatic pressure, i.e., when the switch is open indicative of the door being closed. The valve operator may be a conventionally manually operated valve handle which controls operation of the motor control valve. The valve handle may be pivotally mounted with respect to the pneumatic cylinder, such that when the cylinder rod is fitted within a detent, movement of the handle controls the operation of the motor control valve. When the cylinder rod is moved out of the detent, the handle rotates with respect to the pneumatic cylinder and movement of the handle does not affect operation of the motor control valve. Movement of the handle is preferably restricted by a conventional stopping member, such as one or more chains, thereby preventing the operator from operating the motor control valve when the cylinder rod is out of the detent.
According to the method of the invention, the motor control valve is operated by the handle or other valve operator, which in turn is rendered operative or inoperative by a pneumatic cylinder or other fluid pressure responsive member. The pneumatic cylinder may be supplied with pressurized air when the switch is open, indicative of a door closed position. Accordingly, the door must first be closed before movement of the valve operator will allow hydraulic fluid to pass to the motor which rotates the ring. Moreover, once the door is opened, operator intervention is required to reset the handle in a position such that the hydraulic cylinder will allow operation of the motor control valve in response to the valve operator. This resetting feature desirably ensures that the tong motor cannot be operated after the door is opened while the tong is powered, then the door again closed. The operator must first reset the handle in a position whereby it may subsequently be moved to activate the motor control valve.
It is an object of the present invention to provide an improved system for operating an open throat power tong which improves tong safety by disengaging operation of the hydraulic motor when the door is open and wherein the control system does not require altering or tying into the conventional fluid power system which supplies hydraulic fluid pumped from the hydraulic fluid source to the motor and then back to the hydraulic fluid source.
It is a further feature of the invention that the system and method of the present invention desirably do not require electronic operated components, which are generally considered undesirable when the power tong is operated in the potentially hazardous environment of the hydrocarbon recovery well.
A significant feature of the invention is that tong safety is improved by requiring that the operator reset the handle or other valve operator prior to the valve operator movement controlling the motor control valve.
Still another feature of the invention is that the safety features of the invention allow the operator to easily and quickly determine that the safety system components are operating properly by ensuring that the valve operator can only control a motor control valve when the door is properly closed.
A related feature of the invention is that the safety system of the present invention utilizes inexpensive components which are relatively rugged, and may be easily field serviced.
Still another feature of the invention is that the system of the present invention provides a quick response time to disengage operation of the hydraulic motor if the switch signals that the door has moved out of the fully closed position.
An advantage of this invention is that the switch which controls operation of the safety system may be positioned at various locations on the frame of the power tong, and preferably may be spaced away from the vicinity of the door and rearward of a centerline of the rotary ring.
Still another feature of the invention is that the fluid pressure responsive member preferably is supplied with pneumatic fluid pressure, which allows the safety system to be easily installed and field serviced.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.